1. Field of the Invention
The present invention relates to a light guiding plate used in a backlight apparatus for a liquid crystal display (LCD), and the like. Specifically, the present invention relates to a light guiding plate having improvements in front luminance of a light emitting surface, as well as a backlight apparatus provided with the aforesaid light guiding plate.
2. Description of the Related Art
Backlight units that serve as a backlight apparatus for liquid crystal display are in demand and produced in large quantities along with the spread of electronic equipment having a liquid crystal display thereon. The backlight units are mainly formed by a light source, and a light guiding plate for guiding and causing surface emission of light emitted from the light source.
As the light source, fluorescent tubes, light emitting diodes (LED), or the like are used. Especially when mounted on electronic equipment with smaller and thinner form, the light emitting diode is often used.
As shown in FIG. 19, a backlight unit 100, which uses light emitting diodes as the light source, is generally provided with a light guiding plate 80, a plurality of light emitting diodes such as three light emitting diodes 90a, 90b, and 90c, a reflecting sheet 101, a diffusing sheet 102, a first lens sheet 103, and a second lens sheet 104.
The backlight unit 100 is constructed as follows: the light emitting diodes 90a, 90b, and 90c are disposed at a predetermine pitch on a light incident surface 81 of the light guiding plate 80 such that light emitting surfaces 91a, 91b, and 91c are tightly attached thereto; the reflecting sheet 101 is disposed on the light reflecting surface 82 side of the light guiding plate 80; the diffusing sheet 102, the first lens sheet 103 and the second lens sheet 104 are disposed by overlying them in order of mention on a light emitting surface 83 of the light guiding plate 80, and these are housed and assembled in a casing that is not shown. In the following description, the light emitting diodes 90a, 90b and 90c are also generally referred to as a “light emitting diode 90.”
The light that is incident on the light incident surface 81 of the light guiding plate 80 from the light emitting diode 90 is guided while causing total reflection with the internal surfaces of the light reflecting surface 82 and the light emitting surface 83 in the light guiding plate 80. On the light reflecting surface 82 of the light guiding plate 80, there are formed a prism pattern for efficiently reflecting upward direction the incident light in the direction of the light emitting surface 83, a dot pattern, and the like. The light incident in a critical angle onto the internal surface of the light emitting surface 83 by these patterns is then emitted from the light emitting surface 83.
The light emitted from the light emitting surface 83, due to considerable variations in the distribution of in-plane light amount, is incident on the diffusing sheet 102 for purposes of homogenization.
The light emitted from the diffusing sheet 102 is deflected so as to enter the first lens sheet 103 and the second lens sheet 104, and condense in the normal direction of the light emitting surface 83.
The directional components of lights, which the first lens sheet 103 and the second lens sheet 104 condense the light passed through the diffusing sheet 102, are different from each other.
The first lens sheet 103 is also called Y direction lens sheet, which is a lens sheet to have the component of the light in the Y axis direction and condense in the normal direction of the light emitting surface 83, when the light guiding plate 80 provided with the light emitting diode 90 is arranged on an X-Y coordinate plane such that the light emitting surface 83 becomes the front, as shown in FIG. 20. On the other hand, the second lens sheet 104 is also called an X direction lens sheet, which is a lens sheet to have the component of the light in the X axis direction shown in FIG. 20 and condense in the normal direction of the light emitting surface 83.
Thus, the front luminance of the backlight unit 100 may be improved efficiently by having the light emitted from the light emitting surface 83 of the light guiding plate 80 and passed through the diffusing sheet 102 pass through the first lens sheet 103 and the second lens sheet 104.
The reflecting sheet 101 disposed on the light reflecting surface 82 side of the light guiding plate 80 functions to reflect the light escaped to the outside of the light reflecting surface 82 so as to bring back to the light guiding plate 80, when the light guiding plate 80 guides the light incident from the light incident surface 81 while causing total reflection.
For example, on of such related art is disclosed by Japanese Patent Application Publication No. 2003-35910.